An autopsy completed this week found that Elizabeth Holder died Jan. 19 of endomyocardial fibrosis, aggravated by a severe case of tonsillitis.

"She wouldn't have known that she had the endomyocardial fibrosis," which is marked by a change in heart tissue and generally caused by previous viral infections, said Bill Pellan, director of investigations at the Pinellas-Pasco Medical Examiner's Office.

Eight days before she died, Pinellas deputies had placed Elizabeth and her 2-year-old sister into foster care after their mother was charged with neglect.

Although initial reports indicated a medical event prompted the girl's death, an investigation revealed sheriff's employees broke a state rule requiring that children placed in foster care get a medical screening within 72 hours.

Elizabeth never got a screening.

Elizabeth's heart condition likely would not have been picked up by a casual health screening, officials told the Tampa Bay Times on Friday. Tonsillitis, however, might have been detected.

"That event of the tonsillitis would have caused the heart to go into some type of arrhythmia," Pellan said Friday. "That would have triggered a cardiac event because she had the underlying disease. That's the most probable chain of events."

Pellan said investigators were not able to determine how long Elizabeth had the disease or the tonsillitis, a common condition in children.

Pinellas authorities said the girl never complained of being sick while in foster care. Tonsillitis symptoms can include fever and sore throat.

Authorities said they could not say if the outcome would have been different if Elizabeth's tonsillitis had been discovered.

The girl was taken from her parents' care on Jan. 11 after a neighbor saw her wandering unattended at the Gulf to Bay Mobile Home Park near Clearwater.

Pinellas deputies said Elizabeth's mother and father were high on prescription pills at the time.

Eight days after the children were placed in foster case, they were at a babysitter's in Dunedin when Elizabeth began clutching her head.

"She began to scream, 'It hurts! It hurts! It hurts!'" Pinellas Sheriff Bob Gualtieri told reporters at a news conference shortly after the girl's death.

Elizabeth went limp and was pronounced dead at a local hospital.

"I hope that the fact that (the screening) did not happen did not make a difference," Gualtieri said Friday. "To me it doesn't matter. Even if there was no causation we were still wrong. I take responsibility for that. We should have done it, and we own it."

Gualtieri launched an internal investigation after it became clear his agency had violated the three-day rule. A family support worker at the agency, which handles child protection investigations in Pinellas County, tried to get the children a health screening but made the doctor's appointments for Jan. 22 and Jan. 24 after offices said they were booked solid before then.

Gualtieri said the internal review was still ongoing, but that the department already made policy changes.

"We've expanded the network of the providers we can take the kids to," Gualtieri said,

The state Department of Children and Families' investigation is not yet complete, spokeswoman Terri Durdaller said Friday.

Elizabeth's family could not be reached for comment.

After the girl died, her grandmother said she believed the girl suffered a brain aneurysm based on hospital staff statements.

Nothing suggestive of an aneurysm was found in the autopsy.

Times researcher Natalie Watson contributed to this report. Kameel Stanley can be reached at kstanley@tampabay.com or (727) 893-8643.